The present invention relates to a method and apparatus for controlling the transmission of a vehicle wherein the shifting of the transmission is controlled by means of an electronic control circuit.
The laid-open publication of Japanese Application No. 84450/1986 discloses a four-speed transmission of a purely hydraulic control type which is adapted to effect a speed change or shifting by changing over a shift valve by means of throttle pressure corresponding to the throttle opening of the engine and governor pressure corresponding to the vehicle speed. The transmission has a first automatic speed-change range and a second automatic speed-change range. In the just-described structural arrangement, when the first automatic speed-change range has been selected, an automatic speed-change or shifting from a first-speed stage or the lowest speed up to a fourth-speed stage, or the highest speed is effected or takes place in accordance with a predetermined speed change characteristic responsive or relative to the running condition of the vehicle. As with the above-described structural arrangement, when the second automatic speed-change range has been selected, the automatic speed change or shifting from the first-speed stage up to the third-speed stage is effected or takes place in accordance with the same speed-change characteristics as in the first automatic speed-change range, except that the third-speed stage is continuously held even in the range where the fourth-speed stage is usually established. Thus, when a need arises to reduce the speed while in high-speed running at the fourth-speed stage in the first automatic speed-change range, the third-speed stage is established by changing over to the second automatic speed-change range, thereby enabling engine braking to be applied.
Transmissions which use an electronic control circuitry such as a microcomputer to change over the shift valve for a speed change operation have recently been developed because such a control system makes it easier to carry out a finer speed change control according to the running state of a vehicle and to change the speed-change characteristics according to the type of vehicle. In an electronic control-type transmission, when two automatic speed-change ranges are provided, as described above, it becomes possible to effect an automatic speed change in each range according to its specific speed-change characteristics, the characteristics of each range being different from the other. In this case, it is desirable to make it possible to effect an automatic speed change from the first-speed stage up to the fourth-speed stage in the second automatic speed-change range as well, thereby allowing the user to select speed-change characteristics in accordance with his or her own preference.